feat(config): add support for fallback formatters

[hougesen]

This pr adds support for global formatters that are ran on all snippets, and fallback formatters which are only ran on files with no existing formatter (or global formatters).

* is used to signify global formatters.

• Fallback formatter

{
  "languages": {
    "*": "typos"
  }
}

_ is used for fallback formatters.

{
  "languages": {
    "_": "prettier"
  }
}

[hougesen]

Glad you like it 😄